This invention relates to an objective lens driving device suitable for use in an optical pickup of an optical disc drive or the like, and further relates to an optical pickup using it.
An optical disc drive is a device for reading or writing information from or into an optical disc (CD, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD+R, DVD−R, DVD-RAM, DVD+RW, DVD−RW, Blu-ray, AOD, or the like). In order to achieve reading or writing the information from or into the optical disc, the optical disc drive of this type comprises an optical pickup for irradiating a laser beam onto the optical disc and detecting its reflected light.
In general, an optical pickup comprises a laser beam source for emitting a laser beam and an optical system for guiding the emitted laser beam to an optical disc and further guiding its reflected light to a photodetector. This optical system includes an objective lens disposed so as to confront the optical disc.
It is necessary that the objective lens used in the optical pickup be accurately controlled in position with respect to a focus direction along an optical axis and a track direction along a radial direction of the optical disc to thereby accurately focus a laser beam on a track of a recording surface of the rotating optical disc. These controls are called a focusing control and a tracking control, respectively. Further, following improvement in recoding density, there have recently been increasing demands for removing or suppressing the influence caused by warping of the optical disc. In view of this, it is also necessary that the objective lens be subjected to a so-called tilting control.
In an objective lens driving device of this type, a lens holder holding the objective lens is elastically supported by a plurality of suspension wires for enabling the focusing control, the tracking control, and the tilting control. Further, focusing coils, tracking coils, and tilting coils are attached to the lens holder. These coils are partly located in gaps of a magnetic circuit. With this structure, the conventional objective lens driving device is capable of finely controlling a position and an inclination of the objective lens by controlling currents flowing through the respective coils.
Recently, there has been available a super thin type optical disc drive called an ultra slim drive. In the super thin type optical disc drive of this type, an objective lens driving device is normally configured as a so-called asymmetry type. With this asymmetry type objective lens driving device, acceleration sensitivity can be enhanced, but it is quite difficult to prevent occurrence of undesired resonance such as rolling, pitching, or yawing of an objective lens.
On the other hand, it has also been proposed to configure an objective lens driving device as a so-called symmetry type (see, e.g. JP 2001-93177 A). With this symmetry type objective lens driving device, it is easy to prevent occurrence of undesired resonance of an objective lens.
In addition, an optical pickup actuator of which manufacturing cost is reduced by decreasing the quantity of used damper material has been proposed (see, e.g. JP 2003-151157 A). According to JP 2003-151157 A, the optical pickup actuator comprises a movable part with an objective lens and a fixed part with a holding part connected to the movable part with at least two suspension wires. The movable part is relatively moved with respect to the fixed part by means of magnetic driving means. The holding part is provided with grooves which are provided on the opposing face sides and through which respective suspension wires are inserted, and a damper material furnished in the grooves. However, JP 2003-151157 A neither discloses nor teaches an optimal damper material applied position in order to obtain a moderate damping effect.